The present invention relates to dual pressure fractionating processes. More particularly, the present invention relates to an improved dual pressure fractionating process for hydrocarbons such as for example the depropanization of hydrocarbons.
The use of so-called "dual pressure" fractionating of hydrocarbons has been used, with great success, for the depropanization of hydrocarbons. The dual pressure process, which is described in detail in U.S. Pat. No. 3,783,126 (herein incorporated by reference for all purposes) eliminates many of the problems associated with prior art depropanizer processes. For one, polymerization of highly unsaturated compounds within the fractionating column is largely eliminated. Using the dual pressure process, and as applied to the depropanization of hydrocarbons, temperature and pressure conditions in the high pressure section of the fractionating column can be chosen to be compatible with optimum vaporization of the C.sub.3 's and condensation of the vapors at easily attainable temperatures. Additionally, temperatures and pressures in the low pressure section of the fractionating column can be chosen to achieve a temperature which will minimize polymerization of the bottoms fraction in the low pressure section. As the cited patent points out, other advantages are achieved using the dual pressure process.
Although the dual pressure process possesses many advantages, there are certain inherent disadvantages, at least one of which is potentially dangerous. It has been found that when the process is used in the depropanization of hydrocarbons, there is a tendency for certain unstable components to accumulate or build-up in the high pressure section of the fractionating column, usually in the lower section thereof. These unstable components, which vary depending upon the nature of the feed to the fractionating column, are generally highly unsaturated in nature, e.g. acetylenes, dienes and the like. It is known that high concentrations of such highly unstable components can be detonated in the absence of oxygen, if subjected to elevated temperatures and pressures. Moreover, detonation of such unstable components can occur at lower concentrations and lower system temperatures and pressures if an ignition source is present. Such ignition source can be provided, for example, by static electrictiy caused by high fluid flows in the column, highly exothermic polymerization and other type reactions, etc.